The present invention relates to a method and apparatus for controlling the idling speed of an internal combustion engine during the starting operation and warm-up period of the engine.
In the past, various control methods have been proposed in which a basic control variable is preliminarily established to control the idle air flow to the engine for controlling idling speed of the engine according to the engine warm-up conditions such as the cooling water temperatures and the idle air flow is adjusted in accordance with the basic control variable. However, since these known methods are designed so that during the warm-up period a control variable is unambiguously derived from a single map in accordance with the warming condition of the engine and the control variable is outputted to effect an open-loop control of the idling speed, this type of control finds it difficult to adapt the control to the required starting and warm-up characteristics of the engine and thus various problems still remain unsolved. For instance, one type of generating a fixed amount of control variable irrespective of engine warm-up conditions in the starting period of the engine undergoes such a problem that the engine speed is increased abnormally if the fixed amount of control variable is generated after the warm-up of the engine has been completed and that the engine speed is not increased quickly leading to the engine stalling in very cold condition. The problem with using only one kind of control variable varying in accordance with the warming conditions during the warm-up period is that it is difficult to effect a control which responds to decrease in the engine frictional torque so that even under the same warming-up condition (or water temperature), lower the starting temperature is, higher the engine speed tends to become thus making it difficult to adapt the engine speed after the starting to the warming conditions of the engine.